Reproduction processes are known wherein positive-working photopolymerizable elements and negative-working photosensitive elements are exposed imagewise through an original forming nontacky and tacky image areas. Positive-working photopolymerizable elements are described in Chu and Cohen U.S. Pat. No. 3,649,268 and negative-working photosensitive elements are described in Cohen and Fan U.S. Pat. Nos. 4,174,216 and 4,191,572. The image is developed by toning with a suitable toner which desirably adheres only in the tacky image areas. Excess toner which may be present is removed from the nontacky areas to provide, for example, an image which is a proof of the original of which can be used to transfer the image to another surface. Multilayer proofs such as surprint proofs can be made as well.
In view of the increasing importance of proof-making in the printing industry and the problems inherent therein, improved toners and applicators for applying these toners are desirable. Some recognized improvements in toners are those described in Chu and Manger U.S. Pat. No. 3,620,726, mixtures using these toners described in Gray U.S. Pat. No. 3,909,282 and the toners of Manger, Fickes and Long described in U.S. Pat. No. 4,215,193. From the early use of pads dipped in toners, improved toner applicators are the subject of Sandner U.S. Pat. No. 4,019,821 (hand operated toning) and Tobias U.S. Pat. No. 4,069,791 (automatic toning). Application of any of the above described toners as well as known prior art toners to tacky image areas of phtosensitive elements has the problem that the background color resulting from the toners is difficult to completely remove from the nontacky areas of the said elements. Generally an attempt is made to remove the excess toner from the nontacky areas by means of mechanical action using a cloth, brush or other toner removal means. It is known that static is generated by rubbing dissimilar materials together. Depending on the particular film being toned and the toner removal means, the amount of static formed varies. For example, cleaning brushes closest to the film in the triboelectric table would be expected to generate a relatively low charge. Thus it would be expected that an acrylic brush would generate only a small charge with respect to an element that contains an acrylic compound in its photosensitive layer. The toner, however, can also generate a charge against the brush (or cleaning means) and the photosensitive element. If the toner, cleaning means and element have an identical place in the triboelectric table substantially no static charge would be generated. Such a system, while desirable, is not generally achieved. Despite the aforementioned disadvantage the removal of background color in the nontacky areas is desirable. In manual applications this is time consuming. Cleaning operation in a machine increases the cost thereof. After clean-up, some undesirable stain is usually present in the nontacky areas. The term "background color" as used herein is the color present in the nontacky background areas of an exposed and toned positive-working or negative-working photosensitive element prior to any step being taken to remove toner therefrom. Background color is the sum of two components: "stain" which as used herein is the color which is normally not capable of being removed from the background color areas by exhaustive wiping of the areas, and "clean-up" which as used herein is the color which is normally capable of being removed from the background color areas, e.g., by wiping, air impingement, etc.
Dry nonelectrosopic toners comprising pigmented organic resin particles have been developed which provide good clean-up and are substantially nonstaining in the nontacky areas of the photosensitive elements used to prepare multilayer proofs. Such toners have been surface treated with at least 0.5% by weight of a slip agent, e.g., silicone oil having a weight average molecular weight of about 230 to 50,000; saturated hydrocarbons having a weight average molecular weight of about 200 to 10,000; or fluorocarbon compounds having a weight average molecular weight of about 500 to 500,000, in combination with at least 1% by weight of a defined antistatic agent. The dry nonelectroscopic toner particles are described in Fickes U.S. Pat. No. 4,397,941. The optical density of some toners, e.g., magenta, cyan, tends to be below the density required for prepress proofs. In addition, upon aging the toner, the toned density does not remain stable from proof to proof.
It is desired to provide dry, nonelectroscopic toner particles which when surface coated have clean-up qualities and nonstaining of the nontacky areas of photosensitive elements of quality comparable to known dry nonelectroscopic toner particles and possess high density, particularly on magenta and cyan toners, and excellent density and background color aging stability.